There are numerous categories of bleaches which are well known in the art. Of the wide variety currently available, chlorine releasing bleaches, inorganic peroxygen bleaches, and organic peroxyacid bleaches are the most common. The chlorine releasing bleaches have certain disadvantages associated with their use such as, for example, their tendency to weaken or degrade fabrics, a tendency to react with other components in the composition in which they are present and their general propensity for fading colors in many dyed fabrics. Additionally, under several bleaching conditions chlorine bleaches cause yellowing of certain synthetic fabrics.
While inorganic peroxygen bleaches overcome many of the disadvantages found with chlorine bleaches, they have limitations on use in that they must be used at relatively high temperatures, such as 85.degree. C. or higher. This drawback becomes significant in light of the modern trend of using lower wash temperatures which are generally less than about 60.degree. C. in order to reduce energy costs and prolong the life of the fabric. As a consequence, it is generally necessary to improve the low temperature performances of inorganic peroxygen bleaches through the addition of peroxygen bleach activators also known as peroxyacid precursors.
In the past, ninny have also attempted to use peroxyacid bleaches, either alone or in combination with a bleach activator, as an alternative to the chlorine and inorganic peroxygen bleaches described above. Unfortunately, upon dissolution in water, peroxyacid bleaches such as peroxycarboxylic acids lose their active oxygen and convert to carboxylic acid. Thus, those in the past have found it difficult to formulate stable liquid bleaching compositions.
Many, however, have attempted to stabilize the peroxyacids in their compositions by various means such as encapsulation or incorporation of stabilizing systems. Representative of such attempts include Hardy et al, U.S. Pat. No. 4,536,314; Thompson et al, U.S. Pat. No. 4,539,130; and Burns, U.S. Pat. No. 4,606,838, all of which are commonly assigned. All of these patents are directed to bleaching compositions containing peroxyacids and bleach activators. While the bleaching compositions disclosed therein are suitable for their intended use, they only contemplate compositions in "granular" form as opposed to a stable "aqueous liquid" bleach. Past attempts in this regard, however, have found that it is extremely difficult to formulate a stable aqueous bleach solution based on peroxyacid and/or the combination of a bleach activator and a peroxygen bleach. In addition to the degradation to carboxylic acid problem discussed previously, bleach activator/hydrogen peroxide systems have also exhibited stability problems arising from extraneous reactions with the conventional components of liquid bleaches including solvents, pH adjusting agents, surfactants and soil suspending agents.
To alleviate these problems, attempts have been made to maintain peroxyacids and bleach activators in a suspension or slurry as an alternative to a homogenous liquid bleach system. By way of example, Reuben, U.S. Pat. No. 5,039,447 (Monsanto Company), discloses a pourable sulfone peracid bleaching composition. The composition is an aqueous stable liquid bleach comprising sulfone peroxycarboxylic acid and a stabilizing system including anionic and nonionic surfactants and a salt stabilizer such as sodium sulfate. While this particular bleaching composition may be effective, it has a cloudy appearance not particularly aesthetically pleasing to users. Moreover, because the composition contains the peroxyacid as a solid suspension or slurry, there is a strong likelihood of the solid phase separating from the liquid phase, especially over extended storage periods and across varying temperature conditions. Additionally, the presence of a solid suspension in the bleaching composition increases the viscosity, thereby rendering it less pourable, a feature not especially convenient for users.
Accordingly, there is a continuing need in the art for a stable aqueous liquid bleach composition which can be used as an additive. There is also a need in the art for such a stable liquid bleach composition which is isotropic or in a single phase and is translucent in appearance. Further, it would be desirable to have a liquid bleach composition having a lower viscosity so as to facilitate pouring of the bleach into the washing solution.